DSA · Theory

Construct BST from its given level order traversal

Theory

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Construct BST from its given level order traversal

Meera only reaches for Construct BST from its given level order traversal when folder on disk has to stay correct in a file explorer.

Construct BST from its given level order traversal on the board: left < root < right. Then say what folder on disk looks like after.

Without Construct BST from its given level order traversal, a file explorer gets messy and folder on disk is hard to trust.

Use Construct BST from its given level order traversal when folder on disk must stay clear. If a simpler DSA step works, use that instead.

Don’t do this with Construct BST from its given level order traversal: unbalanced BST becoming a list. Interviewers spot it in ten seconds.

After Construct BST from its given level order traversal, Meera should still remember unbalanced BST becoming a list.

Viva for Construct BST from its given level order traversal: what it is → left < root < right → the mistake (unbalanced BST becoming a list).

Diagram

Exam tip

Say Construct BST from its given level order traversal in one breath, then left < root < right, then unbalanced BST becoming a list.

Example

class Node:
    def __init__(self, val):
        self.val = val
        self.left = None
        self.right = None

def insert(root, val):
    if root is None:
        return Node(val)
    if val < root.val:
        root.left = insert(root.left, val)
    elif val > root.val:
        root.right = insert(root.right, val)
    return root

root = None
for v in [5, 2, 7, 1]:
    root = insert(root, v)
print(root.val, root.left.val, root.right.val)

Construct BST from its given level order traversal — bST invariant: left < node < right — enables log-time search when balanced.

Short notes

DefConstruct BST from its given level order traversal — Meera uses it for folder on disk in a file explorer.
RuleConstruct BST from its given level order traversal → left < root < right.
RememberConstruct BST from its given level order traversal + Big-O (a file explorer).
UseConstruct BST from its given level order traversal in a file explorer (folder on disk).
TrapConstruct BST from its given level order traversal — unbalanced BST becoming a list.
ExConstruct BST from its given level order traversal → folder on disk.

class Node: def __init__(self, val): self.val = val self.left = None self.right = None def insert(root, val): if root is None: return Node(val) if val < root.val: root.left = insert(root.left, val) elif val > root.val: root.right = insert(root.right, val) return root root = None for v in [5, 2, 7, 1]: root = insert(root, v) print(root.val, root.left.val, root.right.val)

Construct BST from its given level order traversal

Example

Short notes

Questions

Construct BST from its given level order traversal

Example

Short notes

Questions